FIG. 1 is a structural schematic diagram of an array substrate in the prior art. As shown in FIG. 1, the array substrate in the prior art comprises a gate electrode 2, a gate insulation layer (GI) 3, an active layer 4, ohmic contact layers 5, a source electrode 61 and a drain electrode 62 which are sequentially arranged on a substrate 1, and a pixel electrode (ITO) 7 which is lapped on the upper surfaces of the drain electrode 62 and the gate insulation layer 3.
Under normal circumstances, the preparation method for the array substrate is: forming the gate electrode 2 on the substrate 1 at first; then forming the gate insulation layer 3, the active layer 4 and the ohmic contact layers 5; then forming the source electrode 61 and the drain electrode 62; and finally forming the pixel electrode 7.
During the process of forming the source electrode 61 and the drain electrode 62, a wet etching process is adopted, although wet etching is simple and convenient to operate and has low requirements on equipment, the anisotropy of the chemical reactions thereof is poor, the line width of a pattern on a film is less than that of a pattern on an anti-corrosion agent film due to transversal etching, and therefore, accurate control performance is poor. Anisotropy is also referred to as non-uniformity, and means that all or a part of physicochemical properties of an object represent difference to a certain extent respectively with different directions, one important characteristic that an ideal etching process needs to have is good aeolotropic etching, that is, only vertical etching exists and no transversal etching exists. In this way, accurate etching on the etched film for a geometric pattern which is identical to that on the anti-corrosion agent film can be ensured.
In the prior art, during a preparation process of the source electrode 61 and the drain electrode 62, the anisotropy and accurate control performance of wet etching are poor, therefore, a gradient angle a formed on the side surface of the drain electrode 62 after the etching is finished is large, and the gradient angle a is in a range of 80-90 degrees; meanwhile, the thicknesses of the source electrode metal layer and the drain electrode metal layer are in a range of 2000-4000 Å, the pixel electrode metal layer is thin, and the thickness thereof is in a range of 400-700 Å, therefore, during deposition for the pixel electrode metal layer, the slip-down occurs on the side surface of the gradient angle a due to gravity action, thus the pixel electrode metal layer herein is thin and even is broken, poor lap joint for the formed pixel electrode 7 and drain electrode 62 is easily caused, and product quality is seriously influenced.
Therefore, the technical problem to be solved by a person skilled in the art is how to provide a preparation method for an array substrate, which is capable of facilitating lap joint for a pixel electrode and a drain electrode.